In recent years paper and paper product manufacturers have recognized that variants of technology commonly used in paper production can be adapted for making fabrics of inexpensive and durable form. Manufacturers recognize that acceptable substitutes for fabrics made by weaving continuous fiber filaments in the conventional manner can be found in non-woven fabrics produced by processes such as wet-laying synthetic fiber filaments with paper-making equipment.
In the wet-laying process, an aqueous dispersion containing synthetic fiber filaments of predetermined diameter, length and rigidity is distributed over a moving wire or web. The fiber filaments accumulate on the advancing web as the dispersion liquid drains away. The result is a layer of fabric composed of intertwined fibers. To enhance fabric strength, manufacturer may add binding agents to the formed sheet to improve fiber cohesion. Description of typical wet-laying processes using paper-making equipment can be found in U.S. Pat. No. 3,808,095, and U.S. Pat. No. 3,839,142.
Manufacturers however have encountered difficulties in making non-wovens by wet-laying synthetic fibers. For example, during processing, manufacturers have found that fibers initially introduced to establish the dispersion may fail to completely separate, or, once separated, may be caused to interact and entangle. Fibers may fail to initially disperse as a result of cohesion caused by defects in the fibers created when they are first sliced to the desired lengths. Heat generated in slicing can distort the fiber ends causing either burrs to mechanically bind the fibers or welds to physically join them. Failure of the fibers to separate results in fiber bundles within the dispersion. Further, once separated, fiber defects may act as catches to snare and entangle fibers as they come in contact. Additionally, the very turbulence initially necessary to separate the fibers can cause continued interaction between the fibers resulting in lumps much in the way hair in water interacts and entangles.
The tendency for fibers to lump and entangle in turbulence is particularly a problem where manufacturers have attempted to improve fabric characteristics such as strength, softness of hand and drape by using thin, long and flexible fibers. Particularly where long thin and flexible fibers having length to diameter ratios of 400 to 3000 and higher, as for example 1.5 denier by one inch and 3.0 denier by one and one half inches, are used to improve fabric characteristics, manufacturers have found a substantial increase in the tendency for the fibers to entangle themselves into lumps.
Fiber bundles and lumps once present in the dispersion due to failure to initially separate or to subsequent entanglement give rise to nonuniformity in the fabric sheet. As the dispersion is introduced to and the fibers laid upon the web, the bundles and lumps tend to disrupt even distribution of fiber over the web, producing regions of high and low fiber density. The result is a nonuniform and weak fabric which is commercially unacceptable.
Manufacturers have therefore endeavored to establish and maintain dispersion of the fiber filaments during processing. In an attempt to obtain uniformity, manufacturers have in the past used chemical agents to disperse the fibers and maintain them dispersed. Particularly, foam agents have been suggested for this purpose. However foams have been found difficult to use. Particularly, during processing, manufacturers have found over agitated foams float the fiber filaments out of the dispersion, depleting the dispersion of fibers. Additionally, foams are undesirably expensive.
As an alternative, liquid agents have also been tried. Hereto, however, drawbacks have been encountered. Particularly, those liquid agents which enhance the dispersion of long individual fibers cannot disperse fibers with welded ends due to poor cutting or multiple fiber rods which are the result of poor spinning. Additionally, it is found that there can occur certain small percentages of over length fibers, e.g. 2.times. and 3.times. specified length, which under prolonged agitation will form tangles and clumps. As a result, liquid agents have not completely solved the dispersion and subsequent entangling problems associated with thin, long and flexible fibers.
Further description and explanation of the nature of non-woven fabric making by wet-laying, the difficulties encountered with thin, long and flexible synthetic fibers in aqueous dispersions and the use of chemical agents as possible solutions may be found in U.S. Pat. No. 4,049,491 to Ring et al., entitled "Viscous Dispersion for Forming Wet-Laid, Non-Woven Fabrics" filed Feb. 20, 1975 and issued Sept. 20, 1977.